"Our requirements are narrow. We prohibit the use of GenAI models which are trained on content without the permission of its creators. This rule prohibits the use of the most popular GenAI products. For example: DALL-E, ChatGPT, Stable Diffusion, Midjourney, and GitHub Copilot are all prohibited.": https://screamzone.org/wiki/policies/generative-ai
That answers that.
If you want a Game Jam that allows AI tools within reason (and is Halloween themed), you can join the "Themed Horror Game Jam": https://itch.io/jam/themed-horror-game-jam-22, which starts in ~4 days, or the "GameDev.tv Halloween Jam 2025": https://itch.io/jam/gamedevtv-halloween-jam-2025, which starts around the same time this one does.